The invention relates to a holding apparatus being adapted to electrostatically hold a component, in particular a silicon wafer. The invention relates also to a method for producing the holding apparatus. Applications of the invention are in the provision of devices or tools for holding components by means of electrostatic forces, in particular for holding semiconductor components, for example silicon wafers.
Holding apparatuses for holding components electrostatically, which are also referred to as electrostatic holding apparatuses, electrostatic clamping apparatuses, electrostatic clamps, ESCs or electrostatic chucks, are known in general. An important application of electrostatic holding apparatuses is in holding silicon wafers in lithographic semiconductor processing, for example in chip production, in which the particular advantages of electrostatic holding, such as the ease of switching of electrostatic holding or clamping forces, a high positioning accuracy and the reliable fixing of silicon wafers, are exploited.
Typically, an electrostatic holding apparatus has a structure having a plurality of plate-type or layer-type elements that fulfil differing functions (see e.g. US 2013/0308116 A1). At least one plate-type element (referred to as a first plate in the following) performs the electrostatic holding function of the holding apparatus. For this purpose, the first plate is equipped with an electrode device, by means of which the electrostatic holding forces are generated. According to US 2013/0308116 A1, the electrode device comprises a plurality of electrodes which are embedded in the first plate. At least one further plate-type element (referred to as a second plate in the following) performs a carrying and cooling function. The second plate is produced from a mechanically stiff ceramic, for example, and is fixedly connected to the first plate. The electrostatic holding apparatus has on its upper side a plurality of projecting, upper burls which form a support surface for the silicon wafer and are integrally connected to the second plate, for example according to US 2013/0308116 A1.
A conventional electrostatic holding apparatus, for example according to U.S. Pat. No. 4,502,094 A or US 2013/0308116 A1, has the following disadvantages. The production of the holding apparatus is complex because of the embedding of the electrodes into the first plate. The electrodes each require a separate connection, likewise embedded into the first plate, for applying a clamping voltage. As a result, the electrostatic holding forces can be distributed inhomogeneously along the support surface and may exhibit a change over time (ageing). The embedded electrodes are at a relatively large distance from the component to be held and therefore require a high clamping voltage.
The mentioned disadvantages occur not only in the case of electrostatic holding apparatuses for silicon wafers, but also in the case of holding apparatuses having embedded electrodes, such as, for example, for glass plates having a transparent electrode (ITO), which form substrates for AMLCD, for example.